re, B

by

e a

), m

i-pr

ma

y m

a r

ning

bioethanol, both of which can be used as transport fuel. Other potential products include hydrogen,

polymers and a wide range of value-added chemicals, making this technology important in a post-

petrochemical world. Bioreneries could use cogeneration to produce electricity. The paper identies a

he fewdium-se gasiting inalanceso theirons Bis_facts

through a number of conversion routes. Several types of product

micro-algae for feedstock supply (Carlsson et al., EPOBIO, 2007).

erna-, the

Obligation (RTFO) http://www.dft.gov.uk/pgr/roads/environment/

ARTICLE IN PRESS

Contents lists availab

.el

Energy P

Energy Policy 36 (2008) 44064409factsheet.pdf); Global Bioenergy Partnership: www.globalbioenergy.are those of the author(s), are independent of Government, and do not constitute

Government policy.Current products include bioethanol, biodiesel and other bio- rtfo/). The UK is moving towards the development of transportbiofuels with a target of replacing 5.75 per cent by volume ofpetroleum-based fuels (as at April 2008) by 2010 (United NationsBiofuel Initiative: www.unfoundation.org/les/2006/biofuels_

org/), but recent concerns over sustainability have resulted in are-analysis and assessment of this target which is now considered

$While the Government Ofce for Science commissioned this review, the views

Tel.: +442380592335; fax: +442380594459.

E-mail address: G.Taylor@soton.ac.uk0301-42

doi:10.1suitable for road and other forms of transportation fuel can beproduced including, in the future, aviation fuel, perhaps using

European Commission has introduced the biofuels directive, towhich the UK has committed: the Renewable Transport Fuelfor UK and EU policy of biofuel deployment (EU, 2008).Liquid biofuels may be made from a variety of biomass sources

UK agricultural landscape.As part of a wide range of measures in response to int

tional agreements to reduce greenhouse gas emissionsnergy Partnership: www.globalbioenergy.org/) and local levels(Renewable Fuels Agency, Gallagher Review (http://www.dft.gov.uk/rfa/reportsandpublications/reviewoftheindirecteffectsofbiofuels.cfm). Further concerns over land displacement have also beenidentied (Searchinger et al., 2008) and have resulted in a pull-back

referred to as second generation bioenergy crops. Hydrogen mayalso be produced from biomass, but this is still at the researchstage. The complexity of these supply chains may hinder thedevelopment of biofuel, but may also be advantageous to the UKas many niche products could emerge from the complex and small1. Background

Liquid biofuels provide one of treplacement in the short to mepotential to offer both greenhousecurity. However, at the time of wrprices and reportedly poor energy bgeneration biofuel crops have led twidely at both global (United Natiunfoundation.org/les/2006/biofuel15/$ - see front matter & 2008 Queens Print

016/j.enpol.2008.09.069range of research and development priorities which must be met if this opportunity is to be exploited fully.

& 2008 Queens Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved.

options for fossil fuelterm. They have thesavings and energymid-2008, rising food, particularly from rstuse being questionedofuel Initiative: www.heet.pdf); Global Bioe-

based products such as biobutanol. Feedstocks are oil-based cropssuch as oil-seed rape, used for the production of biodiesel, andsugar- and starch-based crops such as sugar beet and sugar cane,which are used for the production of bioethanol. Such crops whichhave a food use are often referred to as rst generation bioenergycrops. All lignocellulosic biomass (biomass that is mostly plantcell walls which have a high carbon content) can be convertedto liquid fuels through biological processes (esterication andfermentation) or through thermochemical routes such as pyr-olysis. Such dedicated bioenergy crops with no food use are oftenBiofuels and the biorenery concept$

Gail Taylor

School of Biological Sciences, University of Southampton and UK Energy Research Cent

a r t i c l e i n f o

Keywords:

Biodiesel

Bioethanol

Biofuel co-products

a b s t r a c t

Liquid fuels can be made

crops such as oil-seed rap

generation lignocellulosics

This can include animal b

plant cell (lignocellulosic)

its availability. The UK ma

landscape. There are now

effects are disputed.

The technology of re

journal homepage: wwwer and Controller of HMSO. Publishassett Crescent East, Southampton SO16 7PX, UK

rening a range of biomass materials, including oil-rich and sugar-rich

nd sugar beet, biomass that consists mainly of plant cell walls (second

acro- and micro-alga, or material that would now be discarded as waste.

oducts as well as waste wood and other resources. In the medium-term,

terial is likely to be favoured as the feedstock for bioreneries because of

ake use of a number of these options because of its complex agricultural

ange of targets for biofuel use in the UK, although their environmental

these materials is well known. Possible outputs include biodiesel and

le at ScienceDirect

sevier.com/locate/enpol

olicyed by Elsevier Ltd. All rights reserved.

well as economical and social sustainability and future deploy-

ARTICLE IN PRESS

biof

of cu

t us

t us

icy 3appropriate for 2014, with further analysis of the 2020 target of 10%liquid biofuels at that time. Future targets for biofuel supply willalso depend on the development of a sustainability framework withthe likelihood that greenhouse gas (GHG) mitigation rather thanvolume supply may be used as the accepted metric and that a 45%reduction in GHG emissions relative to fossil fuel will be necessaryin future second generation liquid biofuels. It has been estimatedthat liquid fuel demand in the UK in 2010 will be 44.5 milliontonnes, requiring 2.56 million tonnes of biofuel at that time to meetthe RTFO and providing a carbon saving of approximately 2 milliontonnes. Such targets however depend on net GHG savings and this isquestionable.

In the international market, biodiesel (derived commerciallyfrom vegetable or other plant oils) and bioethanol (derived fromthe fermentation of starch or sugar crops) dominate as the mosttechnically feasible and commercialised alternative renewablefuel sources. Biodiesel can also be derived from animal fats, greaseand tallow, which would otherwise be disposed of as waste.

The UK has seen considerable industry pull in the area ofbiofuels in the last year or so, following the introduction of thebiofuels directive. A summary of some of this activity as at May2007 is shown in the UKERC Bioenergy Research Landscape(ukerc.rl.ac.uk/ERL0304.html) and the planned bioethanol deploy-ments in 2008 are listed in the NNFC report (Black and Vetch,2008, http://www.nnfcc.co.uk/metadot/index.pl?id=7607;isa=

Table 1Summary of feedstock availability in the UK, processing routesmeeting the 2010

Crop type Harvest fraction Feedstock area grown in

2004 (100ha)

Percentage

crop area

Oil-seed rape Seed oil 459 +102

Wheat Straw Currently no

biofuel

Wheat Grain 346 +21

Sugar beet Sugar 202 +202

Waste oil/fat Currently no

biofuel

G. Taylor / Energy PolDBRow;op=show;dbview_id=2539). It is also apparent that thecurrent high price of oil (at the time of writing in 2008) and theperceived likelihood of its continuing are having a marked effecton the development of a biofuel industry. Bauen (2005) showedthat biofuels begin to become nancially competitive over $65 perbarrel of oil, even without considering additional environmentalbenets. One analysis of the UK biomass resource suitable forliquid bioenergy production is given in Table 1. It reveals that it isunlikely that any single supply stream will be adequate to meetthe UK commitment to biofuels for 2010.

Current agricultural practices in the UK suggest that the mainsources of liquid biofuels in the near future will be bioethanolderived fromwheat grain and sugar beet, combined with biodieselfrom oil-seed rape and oil waste products. For dedicated croppingsystems, this analysis reveals that approximately a millionhectares of agricultural land would be required to meet the2010 biofuel target for the UK, more than doubling the areadedicated to oil-seed rape production, and doubling the recoveryof wheat for bioethanol. Table 1 shows that the equivalent of800,000 tonnes of fuel produced from wheat grain is currentlyexported from the UK in most years. Using this material forbioethanol production instead of exporting it would be worth-ments must focus on these issues. In addition, The GallagherReview suggests that no future bioenergy crops should becultivated on agricultural land since this may displace food cropsto pristine environments where other ecosystem services could bewhile. It is probably not feasible to more than double productionof oil-seed rape, the expansion of which has implications for a lossof biodiversity and further intensication.

2. Sustainability

The Royal Society (2008) has published an overview of theissues concerning the sustainability of biofuel supply, as has TheHouse of Commons Audit Committee (2008), to address causalrelationships between rising food prices, ecosystem destruction,and claims that the carbon balance of bioethanol from maize canbe worse than in the use of fossil fuel (Searchinger et al., 2008)once indirect effects on land displacement are considered. In theUK, the Renewable Fuels Agency commissioned the GallagherReview, which reported in June 2008. (www.dft.gov.uk/rfa/reportsandpublications/reviewoftheindirecteffectsofbiofuels.cfm).

All of these studies have highlighted the benets of secondgeneration fuels relative to rst generation and also suggest thatboth good and bad biofuels exist, depending on energy blanace as

uel directive? (Turley et al., 2004)

rrent Fuel proposed

(million tonnes)

Biofuel

0.7 Crushing and esterication of the oil to biodiesel

ed for Breakdown, hydrolysis and fermentation of

lignocellulose to bioethanol

0.8 Breakdown, hydrolysis and fermentation of

starch to bioethanol

0.83 Breakdown, hydrolysis and fermentation of

sugar to bioethanol. A recent suggestion is the

formation of biobutanol from this route

ed for 0.1

6 (2008) 44064409 4407threatened. Biofuel supply to the UK is regulated by the RFA andminimum standards of reporting on greenhouse gas mitigationare required. More than 80 per cent of the current 2.5 per cent byvolume liquid transport fuel from biological sources is imported(Department for Environment, Food and Rural Affairs, 2007), withthe RFA rst monthly data revealing that over 50% of this wasfrom USA corn and Brazilian sugar cane. As yet, the sustainabilityof this supply is reported but largely unregulated. Both the UK andEU will address this issue in the near future, with sustainabilitycriteria emerging (EU Sustainability Criteria for Biofuels: www.foeeurope.org/agrofuels/documents/Proposal_sustainability_criteria_biofuels_27Mar08.pdf).

The evidence suggests that the use of second-generation non-food-dedicated energy crops such as trees and grasses is likely toincrease in the future, since they have a better energy balancethan food crops. They can be grown on land not required forfood, although displacement may still be an issue. Theirimpact has been examined by analysis of the whole-life-cyclefrom eld to fuel, which provides powerful tools for determiningthe relative benets of one biofuel chain over another, althoughsome uncertainties still exist in these approaches (Rowe et al.,2008).

extremely good.

Dif

Ag

Other lignocellulosic resources, such as 200,000 tonnes a year ofwheat straw, are also available. Dedicated lignocellulosic biomasscrops include woody short rotation coppice willow and poplar andmiscanthus grass. Unlike conventional crops such as oil-seed rape,these are low-intensity, low-inputs crops with a much improvedgreenhouse gas balance and other environmental benets such asenhanced biodiversity. All research analysis suggests that per-ennial crops will be favoured over annual crops, since they have agreater seasonal capture of solar energy and again producebiomass without the investment into reproductive structuressuch as grain.

Despite these issues, plants will be used more generally as partof the bio-based economy as we become less dependent on the oil.Plants are the ultimate source of renewable sustainable biopro-ducts, and this extends way beyond simply using plants forenergy. High-quality, low-volume chemicals will be harvestedalongside energy crops. Several such conversion routes arepossible, but the basic feedstock for all second-generation biofuelswill be lignocellulose (UKERC Bioenergy Research Landscape:ukerc.rl.ac.uk/ERL0304.html). Step-wise research challengeslinked to this development are inevitable. At the moment itis extremely difcult to extract and process lignocellulosic

ARTICLE IN PRESS

cy 3linked to policy developments to ensure that environmental as wellas economic drivers are considered in any regulatory framework.

3.4. Conversion technologies

Engineering technologies for bioethanol and biodiesel aremore or less available off the shelf. However, inefcient andexpensive enzymes and chemicals are involved in these processes,and improving on them forms the challenge for future research.

4. The challenge for 2050 and beyond

4.1. Future developments and the necessity for step-change research

discoverymaking the biorenery workassavadirvery dependent on what the bioenergy crop might be replacing.ain, if conversion and production are considered, life-cycleessment may give contrasting results. Research tools are nowilable to ensure correct full-life-cycle analysis and these must beof bare-cycle carbon costs of all the technologies considered above.ferent studies disagree on the greenhouse gas balance of a varietyioenergy cropping systems. The greenhouse gas or carbon costsGivlife3.1. Fundamental plant biology and crop science

Any technology available to increase crop yield per unit land areand inputs, (particularly fertiliser and water) in current and futureclimates should be of value to the future development of the biofuelindustry. More importantly, improving plant qualityfor example,by increasing sugar content or starch content and decreasing proteincontentwill enable efcient processing and extraction for biofuel:

The UK has good expertise in crop science and fundamentalplant biology, but it is only being applied in a limited way tobioenergy cropping systems.

GM technologies and non-GM biotechnology may provide thestep change necessary for future improvements, but publicacceptance of these technologies is still uncertain.

There is considerable interest in the use of micro- and macro-algae (seaweed) as feedstock for biofuel, but scaling andcommercialization of these systems remains challenging. Nowidescale consideration of the environmental impacts of suchdeployment has currently been undertaken.

3.2. Industrial microbiology

New enzymes, plant-based enzymes and better fermentationare examples of how the processes for biofuel production could beimproved. We have good expertise in microbiology but this islargely not being applied to the production of biofuels.

3.3. Environmental impacts

In the UK and Europe, one of the key drivers for investment inbiofuels is environmental. Meeting our commitment to the KyotoProtocol, and developing a low carbon economy are key toGovernment targets (Biofuels Research Advisory Council, 2006).

en this, considerable emphasis is needed on assessing the whole-3. Current status of research

UK biofuels research is fragmented and extremely limited, butcore expertise to address some of the issues, highlighted below, is

G. Taylor / Energy Poli4408Although it is technically possible to meet the 2010 biofuelective target from domestic feedstock resources, it is unlikelythat this target can be achieved with current cropping systems.Part of the problem is that crop rotations determine what crops aparticular farm grows. Space is also a limiting factor. For sugarbeet, current plans assume an extra million hectares of agricul-tural land being available, and the same amount of land again isbeing considered to grow dedicated biomass bioenergy crops forheat and power. This scenario also assumes that no furtherdemand for biofuels will occur, and yet all energy analysissuggests that this is unlikely. Imports of bioethanol and biodieselwill contribute to our net requirement, but in the long term, withfull-life-cycle assessment, are not likely to be environmentallysustainable.

In contrast, the UK has a considerable lignocellulosic biomassresource. Lignocellulose is the intimate mix of plant biomass thatconstitutes the cell walla complex material largely consisting oflignin and cellulose. Up to six million tonnes of forest residuesmay be available in the UK each year, for example, and of this, onlyapproximately a million tonnes is recovered and utilised today(Department for Environment, Food and Rural Affairs, 2007).

Processing

LIGNOCELLULOSEFEEDSTOCK

Gasification

Pulping and processing

SYNGAS

Bioprocessing

Fibre lignin

ChemicalsHeat recoveryElectricity

C-1 chemistry

MethanolMixed alcoholsFischer-TropschDimethyl etherAcetic acidAmmonia.

EthanolHydrogenPolymers

Hydrogen

Paper productsWood productsChemicals

Fig. 1. A conceptual biorenery with lignocellulose feedstock being used for ligninto energy to combustion through thermochemical process, pulp recovery for paper,

gasication for gaseous fuel and biological processing for bioethanol. Other fuels

are also possible.

6 (2008) 44064409feedstocks efciently. Several bottlenecks exist and some areidentied in Fig. 1 (UKERC Bioenergy Research Landscape:ukerc.rl.ac.uk/ERL0304.html; Turley et al., 2004; Bauen, 2005).

4.2. Key scientic advances necessary for the biorenery to work

Challenge: better use of available feedstock.

Plants cell walls are lignin and cellulose. These complexstructures are still far from understood. Fundamental to theirutilisation for bioenergy will be research on understandingconstruction and deconstruction of cell walls (Gomez et al.,2008). Linked to this, a key scientic challenge is to makehydrolysis and fermentation reactions efcient and costeffective at large-scale.Likely to occur: Could occur over a 5-year timescale.Challenge: new designer feedstock and microbial processes forbreakdown.

Fundamental biosciences must be utilised to develop new andnovel plants with different plant characteristics. Prioritiesinclude a new generation of bioenergy plants with enhancedsustainability, yield and altered composition; high-ligninplants for pyrolysis and gasication; and high-cellulose plants

References

Bauen, A., 2005. Evidence to the Stern Committee on global growth of CO2emission from transport, and prospects for new technologies to deliveremissions cuts.

Biofuels Research Advisory Council, 2006. Biofuels in the European Union: A Visionfor 2030 and Beyond. Final Draft Report, 14 March.

Carlsson, A.S., Van Beilen, J.B., Moller, R., Clayton, D., BEPOBIO, 2007. Micro- andmacro-algae: utility for industrial applications. Outputs from the EPOBIO Project,ISBN:13:978-1-872691-29-9 /http://www.epobio.net/news/news070917.htmS(accessed 30 September 2008).

Department for Environment, Food and Rural Affairs, 2007. UK Biomass Strategy.Department for Environment, Food and Rural Affairs, London.

EU Sustainability Criteria for Biofuels: /http://www.foeeurope.org/agrofuels/documents/Proposal_sustainability_criteria_biofuels_27Mar08.pdfS (accessed8 June 2008).

EU tighten sustainability criteria for biofuels and pull back on targets forRTFO /http://www.biofuelstp.eu/news/160908news.pdfS (accessed 30 September2008).

Global Bioenergy Partnership: /http://www.globalbioenergy.org/S (accessed 8June 2008).

Gomez, L.D., Steele-King, C.G., McQueen-Mason, S.J., 2008. Sustainable liquidbiofuel from biomass: the writings on the walls. New Phytologist 178,473485.

House of Commons Environmental Audit Committee, 2008. Are biofuels sustainable?First Report of Session 200708, Vol. 1 /http://image.guardian.co.uk/sys-les/Environment/documents/2008/01/18/EACbiofuelsreport.pdfS (accessed 30September 2008).

reviewoftheindirecteffectsofbiofuels.cfmS (accessed 30 September 2008).Rowe, R.L., Whittaker, J., Chapnman, K., Howard, D., Taylor, G., 2008. Can Biofuels be

sustainable in the UK? A systematic review of life cycle analysis for bioenergy

ARTICLE IN PRESS

G. Taylor / Energy Policy 36 (2008) 44064409 4409levels from modelling microbial function, to predictive experi-ments, systems engineering and pilot-scale and commercialplant.Likely to occur: more speculative but possibly 10 years plus.tion from plants may also be possible. Likely to occur: Five to 10 yearsheavy investment by the US;

BP announced its new Bioenergy Centre to be funded either inthe UK or the US.Challenge: better technologies for the assessment of lignocel-lulose and breakdown processes

Cross-cutting interdisciplinary approaches and new technolo-gies are required to visualise plant cell walls, microbialsystems and their functioning. New computing developmentswill be necessary to enable the biorenery concept, at alland Biofuels /http://www.ukerc.ac.uk/Downloads/PDF/S/Sustainable_LCA.pdfS(accessed 30 September 2008).

Royal Society, 2008. Sustainable Biofuels: Prospects and Challenges. Royal Society,London.

Searchinger, T., Heimlich, R., Houghton, R.A., Dong, F., Elobeid, A., Fabiosa, J., Tokgoz,S., Hays, D., Yu, T.H., 2008. Use of US croplands for biofuels increases greenhousegases through emissions from land-use change. Science 319, 12381240.

Turley, D., Ceddia, G., Bullard, M., Martin, D., 2004. Liquid biofuelsindustrysupport, cost of carbon savings and agricultural implications. Report preparedfor DEFRA Organic Farming and Industrial Crops Division.

UKERC Bioenergy Research Landscape: /http://ukerc.rl.ac.uk/ERL0304.htmlS(accessed 8 June 2008).

United Nations Biofuel Initiative: /http://www.unfoundation.org/les/2006/biofuels_factsheet.pdfS (accessed 8 June 2008).are required. Novel discoveries to improve hydrogen produc- Renewable Fuels Agency, The Gallagher Review of the Indirect Effects of Biofuels.Renewables Fuels Agency, UK /http://www.dft.gov.uk/rfa/reportsandpublications/for bioethanol. This requires a systems biology approachlinking biology to phenotyping to high-throughput computing.New microorganisms and biological routes to plant breakdown

Biofuels and the biorefinery conceptBackgroundSustainabilityCurrent status of researchFundamental plant biology and crop scienceIndustrial microbiologyEnvironmental impactsConversion technologies

The challenge for 2050 and beyondFuture developments and the necessity for step-change research discovery--making the biorefinery workKey scientific advances necessary for the biorefinery to work

References